221561 has 4 divisors (see below), whose sum is σ = 234612. Its totient is φ = 208512.

The previous prime is 221549. The next prime is 221567. The reversal of 221561 is 165122.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 165122 = 2 ⋅82561.

It can be written as a sum of positive squares in 2 ways, for example, as 156025 + 65536 = 395^2 + 256^2 .

It is a cyclic number.

It is not a de Polignac number, because 221561 - 2⁶ = 221497 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (17), and also a Moran number because the ratio is a prime number: 13033 = 221561 / (2 + 2 + 1 + 5 + 6 + 1).

It is a Duffinian number.

It is a Curzon number.

It is a plaindrome in base 15.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 221561.

It is not an unprimeable number, because it can be changed into a prime (221567) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6500 + ... + 6533.

It is an arithmetic number, because the mean of its divisors is an integer number (58653).

2²²¹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

221561 is a deficient number, since it is larger than the sum of its proper divisors (13051).

221561 is a wasteful number, since it uses less digits than its factorization.

221561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13050.

The product of its digits is 120, while the sum is 17.

The square root of 221561 is about 470.7026662342. The cubic root of 221561 is about 60.5105507178.

Adding to 221561 its reverse (165122), we get a palindrome (386683).

The spelling of 221561 in words is "two hundred twenty-one thousand, five hundred sixty-one".